Method for forming semiconductor device structure

ABSTRACT

A method includes forming a first semiconductor layer over a substrate. A second semiconductor layer is formed over the first semiconductor layer. The first semiconductor layer and the second semiconductor layer are etched to form a fin structure that extends from the substrate. The fin structure has a remaining portion of first semiconductor layer and a remaining portion of the second semiconductor layer atop the remaining portion of the first semiconductor layer. A capping layer is formed to wrap around three sides of the fin structure. At least a portion of the capping layer and at least a portion of the remaining portion of the second semiconductor layer in the fin structure are oxidized to form an oxide layer wrapping around three sides of the fin structure.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/629,885, filed Jun. 22, 2017, now U.S. Pat. No. 10,636,910, issuedApr. 28, 2020, which claims priority to U.S. Provisional ApplicationSer. No. 62/512,715, filed May 30, 2017, both of which are hereinincorporated by reference in their entirety.

BACKGROUND

The electronics industry has experienced an ever increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. Accordingly, there is a continuing trend in the semiconductorindustry to manufacture low-cost, high-performance, and low powerconsumption integrated circuits (ICs). These goals have been achieved inlarge part by scaling down semiconductor IC dimensions (e.g., minimumfeature size) and thereby improving production efficiency and loweringassociated costs. However, such scaling has also introduced increasedcomplexity to the semiconductor manufacturing process. Thus, therealization of continued advances in ICs and semiconductor devices callsfor similar advances in semiconductor manufacturing processes andtechnology.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic layout diagram of a semiconductor device structurein accordance with some embodiments of the present disclosure.

FIG. 2A to FIG. 2G are schematic cross-sectional views of intermediatestages in the formation of a semiconductor device structure inaccordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact.

Terms used herein are only used to describe the specific embodiments,which are not used to limit the claims appended herewith. For example,unless limited otherwise, the term “one” or “the” of the single form mayalso represent the plural form. In addition, the present disclosure mayrepeat reference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed. The spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein may likewise be interpretedaccordingly.

It will be understood that, although the terms “first,” “second,” etc.,may be used in the claims to describe various elements and/or features,these elements and/or features should not be limited by these terms, andthese elements and/or features correspondingly described in theembodiments are presented by different reference numbers. These termsare used to distinguish one element and/or feature from another. Forexample, a first element could be termed a second element, and,similarly, a second element could be termed a first element, withoutdeparting from the scope of the embodiments. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Further, spatially relative terms, such as “upper,” “lower,” “on,” andthe like, may be used herein for ease of description to describe oneelement or feature's relationship to another element(s) or feature(s) asillustrated in the figures. The spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. The apparatus maybe otherwise oriented (rotated 90 degrees or at other orientations) andthe spatially relative descriptors used herein may likewise beinterpreted accordingly.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

Embodiments of the present disclosure are directed to a semiconductordevice structure and a method of forming the same. In the semiconductordevice structure, a non-uniform thickness oxide layer with a of theoxide layer. Particularly, a portion of the oxide layer above finstructures is formed by oxidating a portion of an underlying cappinglayer, such that a thickness of the top portion of the oxide layer isincreased without producing an overhang structure at the top portion ofthe oxide layer. In addition, the etching window to a dummy gatestructure can be increased, and damages and notching issues of the finstructure can be avoided when performing the etching process with higherpower to the dummy gate structure, and thus threshold voltage of thegate structure of the final semiconductor device structure is controlledto a desired value according to a design requirement. Further, thecapping layer is formed over the fin structures for providing aprotection function for the fin structures and during the subsequentprocesses (such as forming and removing of a dummy gate structure,forming of a gate structure and a gate dielectric, etc.). A top portionof the capping layer may be at least 3 angstroms, in order to reduce theinterface trap density of the oxide layer. Embodiments of the presentdisclosure provide at least the foregoing advantages for fabricating asemiconductor device, e.g. of 7 nm technology node or beyond.

FIG. 1 is a cross-sectional view of a semiconductor device structure 100in accordance with some embodiments of the present disclosure. In thesemiconductor device structure 100, a substrate 102 is provided, whichmay be a semiconductor substrate, such as a bulk semiconductor, asilicon-on-insulator (SOI) substrate, or the like. In a case of SOIsubstrate, a semiconductor material layer is formed on an insulatorlayer which may be, for example, a buried oxide (BOX) layer, a siliconoxide layer, or the like. The insulator layer is provided on asubstrate, typically a silicon substrate or a glass substrate. Anothersubstrate, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material layer may beformed from, for example, silicon, germanium, silicon carbide, silicongermanium, gallium arsenide, gallium phosphide, gallium arsenidephosphide, indium arsenide, indium phosphide, indium antimonide,aluminium indium arsenide, aluminium gallium arsenide, gallium indiumarsenide, gallium indium phosphide, gallium indium arsenide phosphide,combinations thereof, or another suitable material. In some examples,the substrate 102 includes a silicon germanium layer and a silicon layerlying on the silicon germanium layer.

As shown in FIG. 1, the substrate 102 is separated into two deviceregions, i.e., a P-type device region 102A and an N-type device region102B. An N-type well N-well and a P-type well P-well are on thesubstrate 102 and respectively in the P-type device region 102A and inthe N-type device region 102B. The N-type well N-well and the P-typewell P-well may have dopants of appropriate types. For example, theN-type well N-well may include N-type dopants, such as phosphorus,antimony, arsenic, and/or the like, and the P-type well P-well mayinclude P-type dopants, such as boron, gallium, indium, and/or the like.Each of the N-type well N-well and the P-type well P-well includesprotruded portions, and a liner layer 104 and an isolation feature 106are between two neighboring protruded portions of the N-type well N-welland/or the P-type well P-well. The liner layer 104 is conformal to sidesurfaces of the protruded portions of the N-type well N-well and theP-type well P-well. The liner layer 104 may include silicon nitride,silicon carbide, silicon carbon nitride, silicon oxycarbonitride,combinations thereof, or the like. The isolation feature 106 is formedfor electrically isolating fin structures 108A in the P-type deviceregion 102A from fin structures 108B in the N-type device region 102B.The isolation feature 106 may include flowable oxide, such asphosphosilicate glass (PSG), borosilicate glass (BSG), boron-dopedphosphosilicate glass (BPSG), tetraethyl orthosilicate (TEOS) oxide,titanium nitride, silicon oxycabride (SiOC), or another low-k nonporousdielectric material.

In the P-type device region 102A, the fin structures 108A extend fromthe N-type well N-well, and in the N-type device region 102B, the finstructures 108B extends from the P-type well P-well. The fin structures108A are respectively on the protruded portions of the N-type wellN-well, and the fin structures 108B are respectively on the protrudedportions of the P-type well P-well. The fin structures 108A may include,for example, silicon, germanium, silicon germanium, germanium boron,silicon germanium boron, a III-V material (such as indium antimonide,gallium antimonide, indium gallium antimonide), combinations thereof, orthe like. The fin structures 108B may include, for example, silicon,silicon phosphide, silicon carbide, silicon phosphide carbide,germanium, germanium phosphide, a III-V material (such as indiumphosphide, aluminium arsenide, gallium arsenide, indium arsenide,gallium indium arsenide and aluminium indium arsenide), combinationsthereof, or the like. In addition, the fin structures 108A and 108B aredoped with dopants of appropriate types and concentrations. For example,P-type dopants, such as boron, boron fluorine, silicon, germanium,carbon, zinc, cadmium, beryllium, magnesium, indium, combinationsthereof, and/or the like, may be implanted into the fin structures 108Awith a concentration of about 10¹⁸ atoms/cm³ to about 10²² atoms/cm³,and N-type dopants, such as phosphorus, arsenic, antimony, silicon,germanium, carbon, oxygen, sulfur, selenium, tellurium, combinationsthereof, and/or the like, may be implanted into the fin structures 108Bwith a concentration of about 10¹⁸ atoms/cm³ to about 10²² atoms/cm³.

A capping layer 110 is over the fin structures 108A and 108B, and anoxide layer 112 is over the substrate 102 and covers the isolationfeature 106 and the capping layer 110. As shown in FIG. 1, the cappinglayer 110 includes a top portion 110A and a sidewall portion 110B; thetop portion 110A surrounds a top surface of each of the fin structures108A and 108B, while the sidewall portion 110B surrounds side surface ofeach of the fin structures 108A and 108B. The capping layer 110 mayinclude essential silicon. A thickness T_(110A) of the top portion 110Aand a thickness T_(110B) of the sidewall portion 110B of the cappinglayer 110 may be the same or different. In some embodiments, thethickness T_(110A) of the top portion 110A may be at least 3 angstroms,in order to reduce the interface trap density of the oxide layer 112.Further, the thickness T_(110B) of the sidewall portion 110B may also beat least 3 angstroms.

The oxide layer 112 may include silicon oxide, silicon oxynitride,silicon oxycarbide, combinations thereof, or the like, and may be formedby a deposition process, such as a chemical vapor deposition (CVD)process, a sub-atmospheric CVD (SACVD) process, a physical vapordeposition (PVD) process, an atomic layer deposition (ALD) process, oranother suitable process. In some embodiments, a portion of the oxidelayer 112 is formed by performing an oxidation process on the cappinglayer 110.

The oxide layer 112 includes a top portion 112A and a sidewall portion112B. For example, for the semiconductor device structure 100 of 7 nmtechnology node, a thickness T_(112B) of the sidewall portion 112B maybe about 37 angstroms; for the semiconductor device structure 100 of 5nm technology node or beyond, the thickness T_(112B) of the sidewallportion 112B may be about 26 angstroms or less. A thickness T_(112A) ofthe top portion 112A is greater than the thickness T_(112B) of thesidewall portion 112B. In some embodiments, the thickness T_(112A) ofthe top portion 112A is greater than the thickness T_(112B) of thesidewall portion 112B by about 10 angstroms to about 50 angstroms. Forexample, the thickness T_(112A) of the top portion 112A may be greaterthan the thickness T_(112B) of the sidewall portion 112B by about 15angstroms to about 25 angstroms.

A gate dielectric 114 is over the fin structures 108A and 108B, thecapping layer 110 and the oxide layer 112. As shown in FIG. 1, the gatedielectric 114 covers the top portion 112A and the sidewall portion 112Bof the oxide layer 112. The gate dielectric 114 may include a materialsuch as, but not limited to, silicon oxide, hafnium oxide, titaniumoxide, aluminum oxide, tin oxide, zinc oxide, high-k dielectrics,combinations thereof, and/or the like. In some embodiments, the gatedielectric 114 includes multi-layer structure of, for example, siliconoxide or silicon oxynitride with a high-k dielectric. In alternativeembodiments, an interfacial layer (not shown) may also be formed betweenthe oxide layer 112 and gate dielectric 114.

A gate structure 116 is over the fin structures 108A and 108B, thecapping layer 110, the oxide layer 112 and the gate dielectric 114. Thegate structure 116 may include a metallic material (such as titanium,tantalum, tungsten, aluminum, molybdenum, platinum and hafnium), a metalsilicide material (such as titanium silicide, tantalum silicide,tungsten silicate, molybdenum silicate, nickel silicide and cobaltsilicide), a metal nitride material (such as titanium nitride, tantalumnitride, tungsten nitride, molybdenum silicate, nickel nitride andcobalt nitride), silicided metal nitride (such as titanium siliconnitride, tantalum silicon nitride and tungsten silicon nitride), polysilicon, amorphous silicon, combinations thereof, and/or anothersuitable material.

FIG. 2A to FIG. 2G illustrate cross-sectional views of variousintermediary steps of forming a semiconductor device structure inaccordance with various embodiments. In FIG. 2A, a substrate 202 isillustrated. The substrate 202 may be a semiconductor substrate, such asa bulk semiconductor, an SOI substrate, or the like. In a case of SOIsubstrate, a semiconductor material layer is formed on an insulatorlayer which may be, for example, a BOX layer, a silicon oxide layer, orthe like. The insulator layer is provided on a substrate, typically asilicon substrate or a glass substrate. Another substrate, such as amulti-layered or gradient substrate may also be used. In someembodiments, the semiconductor material layer may be formed from, forexample, silicon, germanium, silicon carbide, silicon germanium, galliumarsenide, gallium phosphide, gallium arsenide phosphide, indiumarsenide, indium phosphide, indium antimonide, aluminium indiumarsenide, aluminium gallium arsenide, gallium indium arsenide, galliumindium phosphide, gallium indium arsenide phosphide, combinationsthereof, or another suitable material.

The substrate 202 includes a P-type device region 202A and an N-typedevice region 202B, and an N-type well N-well and a P-type well P-wellon the substrate 202 are respectively in the P-type device region 202Aand the N-type device region 202B. The N-type well N-well and the P-typewell P-well may be formed by implanting dopants of appropriate typesinto the substrate 202. For example, the N-type well N-well may beformed by implanting N-type dopants, such as phosphorus, antimony,arsenic, and/or the like, and the P-type well P-well may be formed byimplanting P-type dopants, such as boron, gallium, indium, and/or thelike.

Semiconductor layers 204A and 204B are formed over the substrate 202. Asshown in FIG. 2A, the semiconductor layer 204A is formed on the N-typewell N-well and in the P-type device region 202A, and the semiconductorlayer 204B is formed on the P-type well P-well and in the N-type deviceregion 202B. The semiconductor layer 204A may be formed from, forexample, silicon, germanium, silicon germanium, germanium boron, silicongermanium boron, a III-V material (such as indium antimonide, galliumantimonide, indium gallium antimonide), combinations thereof, or thelike. The semiconductor layer 204B may be formed from, for example,silicon, silicon phosphide, silicon carbide, silicon phosphide carbide,germanium, germanium phosphide, a III-V material (such as indiumphosphide, aluminium arsenide, gallium arsenide, indium arsenide,gallium indium arsenide and aluminium indium arsenide), combinationsthereof, or the like. Each of the semiconductor layers 204A and 204B maybe formed by using an epitaxy process, such as a metal-organic (MO) CVDprocess, a liquid phase epitaxy (LPE) process, a vapor phase epitaxy(VPE) process, a molecular beam epitaxy (MBE) process, a selectiveepitaxial growth (SEG) process, combinations thereof, and/or anothersuitable process. Then, the semiconductor layers 204A and 204B are dopedwith dopants of appropriate types and concentrations. For example,P-type dopants, such as boron, boron fluorine, silicon, germanium,carbon, zinc, cadmium, beryllium, magnesium, indium, combinationsthereof, and/or the like, may be implanted into the semiconductor layer204A with a concentration of about 10¹⁸ atoms/cm³ to about 10²²atoms/cm³, and N-type dopants, such as phosphorus, arsenic, antimony,silicon, germanium, carbon, oxygen, sulfur, selenium, tellurium,combinations thereof, and/or the like, may be implanted into thesemiconductor layer 204B with a concentration of about 10¹⁸ atoms/cm³ toabout 10²² atoms/cm³.

In some embodiments, as shown in FIG. 2A, a spacer 206 is formed betweenthe semiconductor layers 204A and 204B, in order to separate thesemiconductor layers 204A and 204B from each other. The spacer 206 maybe formed including a material such as silicon nitride, siliconoxynitride, silicon carbide, and/or the like. Further, a planarizationprocess, such as a chemical mechanical polishing (CMP) process, isperformed to planarize the semiconductor layers 204A and 204B and thespacer 206.

In FIG. 2B, an epitaxial layer 208 is formed over the substrate 202, thesemiconductor layers 204A and 204B and the spacer 206. The epitaxiallayer 208 may be formed from essential silicon, and may be formed by anepitaxial growth process, a CVD process, a PVD process, and/or anothersuitable deposition process. In some embodiments, the epitaxial layer208 is formed with a thickness of about 40 angstroms.

In FIG. 2C, a dielectric layer 210 and a hard mask layer 212 aresequentially formed over the epitaxial layer 208. The dielectric layer210 may be used as an adhesive layer between the epitaxial layer 208 andthe hard mask layer 212, and may be used as a etch stop layer foretching the hard mask layer 212. The dielectric layer 210 may be formedfrom an oxide material, such as silicon oxide, hafnium oxide,combinations thereof, and/or the like, and may be formed by using athermal oxidation process or another suitable process. The hard masklayer 212 may be formed from a nitride material, such as siliconnitride, silicon carbon nitride, titanium nitride, combinations thereof,and/or the like, and may be formed by using a deposition process, suchas a CVD process, a low pressure CVD (LPCVD) process, a plasma enhancedCVD (PECVD) process, a PVD process, an ALD process, combinationsthereof, and/or another suitable process. Then, a patterned photoresistlayer (not shown) is formed over the hard mask layer 212, and an etchingprocess, such as a dry etching process, is performed to remove thespacer 206 and portions of the substrate 202, the semiconductor layers204A and 204B, the epitaxial layer 208, the dielectric layer 210 and thehard mask layer 212, so as to form fin structures 204A′ from thesemiconductor layer 204A and fin structures 204B′ from the semiconductorlayer 204B. In some other embodiments, each of the fin structures 204A′and 204B′ has a width that gradually increases from the top portion tothe lower portion. A pitch between two adjacent fin structures 204A′ or204B′ (e.g. the pitch P between the fin structures 204B′) may be about26 angstrom or less. After forming the fin structures 204A′ and 204B′,the dielectric layer 210 and the hard mask layer 212 are removed by oneor more etching processes and/or another suitable removing process.

In FIG. 2D, a liner layer 214 is formed surrounding a lower portion ofthe side surfaces of each of the fin structures 204A′ and 204B′, and anisolation feature 216 is formed over the substrate 202, the finstructures 204A′ and 204B′ and the liner layer 214. The liner layer 214may be formed from, for example, silicon nitride, silicon carbide,silicon carbon nitride, silicon oxycarbonitride, combinations thereof,or the like, and may be formed by a deposition process (such as a CVDprocess, a PVD process and an ALD process) and a thermal oxidationprocess. The isolation feature 216 is formed for electrically isolatingthe fin structures 204A′ in the P-type device region 202A from the finstructures 204B′ in the N-type device region 202B. The isolation feature216 may be formed including flowable oxide, such as PSG, BSG, BPSG, TEOSoxide, titanium nitride, silicon oxycabride, and/or another low-knonporous dielectric material. The isolation feature 216 may be formedfrom a flowable oxide by using a flowable CVD process or anothersuitable process.

In FIG. 2E, portions of the liner layer 214 and the isolation feature216 above the substrate 202 are removed are removed by using one or moreprocesses, such as a CMP process, an etching back process, combinationsthereof, and/or the like. Next, a capping layer 218 is formedsurrounding side surfaces of the fin structures and on the epitaxiallayer 208. The capping layer 218 and the epitaxial layer 208 provide aprotection function for the fin structures 204A′ and 204B′ during thesubsequent processes. The capping layer 218 may be formed from essentialsilicon by using an ALD process, a plasma enhanced ALD (PEALD) process,or another suitable process.

In FIG. 2F, an oxide layer 220 is formed over the epitaxial layer 208,the isolation feature 216 and the capping layer 218. The oxide layer 220may be formed from silicon oxide, silicon oxynitride, siliconoxycarbide, or a combination thereof, and may be formed by using a CVDprocess, an SACVD process, a PVD process, an ALD process, or anothersuitable process. Then, an oxidation process is performed on theepitaxial layer 208 and the capping layer 218, such that an upperportion of epitaxial layer 208 and the capping layer 218 are oxidated byan oxygen plasma to form an oxide layer 222. Therefore, the overalloxide layer (labeled as “224” in FIG. 2F) includes the oxide layers 220and 222 with reduced silicon variation.

In some embodiments, after the oxidation process, a thickness T₂₁₈ ofthe capping layer 218 is at least 3 angstroms, in order to reduce theinterface trap density of the oxide layer 224. In further embodiments, athickness T₂₀₈ of the remained epitaxial layer 208 is also at least 3angstroms.

As shown in FIG. 2F, the oxide layer 224 includes a top portion 224A anda sidewall portion 224B. For the oxide layer 224, a thickness of a topportion 224A above the epitaxial layer 208 and the capping layer 218 isgreater than a thickness of a sidewall portion 224B. With suchcriterion, overhang issue subsequent processes. A thickness T_(224A) ofthe top portion 224A is greater than a thickness T_(224B) of thesidewall portion 224B. In some embodiments, the thickness T_(224A) ofthe top portion 224A is greater than the thickness T_(224B) of thesidewall portion 224B by about 10 angstroms to about 50 angstroms. Forexample, the thickness T_(224A) of the top portion 224A may be greaterthan the thickness T_(224B) of the sidewall portion 224B by about 15angstroms to about 25 angstroms.

In FIG. 2G, a dummy gate structure 226 is formed over the fin structures204A′ and 204B′, the epitaxial layer 208, the capping layer 218 and theoxide layer 224, a dielectric layer 228 is formed over the dummy gatestructure 226, and a hard mask layer 230 is formed over the dummy gatestructure 226 and the dielectric layer 228. The dummy gate structure 226may be formed from polysilicon, amorphous silicon, combinations thereof,or another suitable material. The dummy gate structure 226 may be formedby using, for example, a CVD process, a PVD process or another suitabledeposition process. The dielectric layer 228 may be formed from an oxidematerial, such as silicon oxide, hafnium oxide, combinations thereof,and/or the like, and may be formed by using a thermal oxidation processor another suitable process. The hard mask layer 230 may be formed froma nitride material, such as silicon nitride, silicon carbon nitride,titanium nitride, combinations thereof, and/or the like, and may beformed by using a deposition process, such as a CVD process, an LPCVDprocess, a PECVD process, a PVD process, an ALD process, combinationsthereof, and/or another suitable process.

After the process illustrated in FIG. 2G, the hard mask layer 230, thedielectric layer 228 and the dummy gate structure 226 may besequentially removed during the subsequent processes, and a gatestructure and a gate dielectric may be formed in the locations of thesubstrate 202 where the dummy gate structure 226 is removed. Thus, thesemiconductor device structure formed by a method in accordance with thepresent disclosure is similar to the semiconductor device structure 100of FIG. 1. Particularly, the feature of non-uniform oxide layerthickness of the oxide layer 224 in accordance with the presentdisclosure provides several advantages. Because a portion of the oxidelayer 224 above the fin structures 204A′ and 204B′ are formed byoxidating the upper portion of the epitaxial layer 208 and the cappinglayer 218, the thickness T_(224A) of the top portion 224A of the oxidelayer 224 is increased without producing an overhang structure at thetop portion 224A of the oxide layer 224. In addition, the etching windowto the dummy gate structure 226 can be increased, and damages andnotching issues of the fin structures 204A′ and 204B′ can be avoidedwhen performing the etching process with higher power to the dummy gatestructure 226, and thus threshold voltage of the gate structure of thefinal semiconductor device structure is controlled to a desired valueaccording to a design requirement.

In accordance with some embodiments, a semiconductor device structureincludes a substrate, a fin structure, a capping layer and an oxidelayer. The substrate has a well. The fin structure extends from thewell. The capping layer surrounds a top surface and side surfaces of thefin structure. The oxide layer is over the substrate and covers thecapping layer. A thickness of a top portion of the oxide layer above thecapping layer is greater than a thickness of a sidewall portion of theoxide layer.

In accordance with certain embodiments, a method of forming asemiconductor device structure includes the following steps. A substrateis provided, which has a well. A semiconductor layer and an epitaxiallayer are formed over the substrate. The semiconductor layer and theepitaxial layer are etched to form a fin structure that extends from thewell. A capping layer is formed surrounding side surfaces of the finstructure and on the epitaxial layer. A first oxide layer is formed overthe capping layer and the substrate. A portion of the capping layer anda portion of the epitaxial layer are oxidized to form a second oxidelayer between the remained epitaxial layer and the first oxide layer.

In accordance with some embodiments, a semiconductor device structureincludes a substrate, a first fin structure, a second fin structure, acapping layer and an oxide layer. The substrate has a first well of afirst type and a second well of a second type different from the firsttype. The first fin structure extends from the first well, and thesecond fin structure extends from the second well. The capping layersurrounds a top surface and side surfaces of each of the first finstructure and the second fin structure. The oxide layer is over thesubstrate and covers the capping layer. A thickness of a top portion ofthe oxide layer above the capping layer is greater than a thickness ofeach of sidewall portions of the oxide layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a first semiconductor layer over a substrate; forming a second semiconductor layer over the first semiconductor layer; etching the first semiconductor layer and the second semiconductor layer to form a fin structure that extends from the substrate, the fin structure having a remaining portion of first semiconductor layer and a remaining portion of the second semiconductor layer atop the remaining portion of the first semiconductor layer; forming a capping layer to wrap around three sides of the fin structure such that the capping layer is in contact with the remaining portion of the first semiconductor layer; and oxidizing at least a portion of the capping layer and at least a portion of the remaining portion of the second semiconductor layer in the fin structure to form an oxide layer wrapping around three sides of the fin structure.
 2. The method of claim 1, further comprising planarizing the first semiconductor layer prior to forming the second semiconductor layer.
 3. The method of claim 1, further comprising forming a spacer layer on a side of the first semiconductor layer prior to forming the second semiconductor layer.
 4. The method of claim 1, wherein the first semiconductor layer is formed from silicon germanium.
 5. The method of claim 1, wherein the second semiconductor layer is formed from silicon.
 6. The method of claim 1, wherein the oxide layer is silicon-containing and/or silicon-germanium-containing.
 7. The method of claim 1, wherein the oxide layer is formed having a thickness of 10 angstroms to 50 angstroms.
 8. The method of claim 1, wherein after the oxidization, a thickness of the remaining portion of the second semiconductor layer and a thickness of a sidewall portion of the capping layer are at least 3 angstroms.
 9. The method of claim 1, further comprising: forming a liner layer conformal to side surfaces of the fin structure; and forming an isolation feature over the substrate and the liner layer.
 10. A method comprising: epitaxially growing a silicon germanium layer over a substrate; performing a chemical mechanical polish (CMP) process to planarize the silicon germanium layer; epitaxially growing an epitaxial layer over the planarized silicon germanium layer; patterning the epitaxial layer and the planarized silicon germanium layer to form a fin structure; forming an isolation feature over the substrate and in contact with the patterned epitaxial layer of the fin structure; recessing the isolation feature; and performing an oxygen plasma process on the fin structure to form an oxide layer having a non-uniform thickness over three sides of a remaining portion of the fin structure.
 11. The method of claim 10, wherein the oxide layer is silicon-containing and/or silicon-germanium-containing.
 12. The method of claim 10, wherein performing the oxygen plasma process is such that the oxide layer is thicker over a top side of the three sides of the remaining portion of the fin structure than over a lateral side of the three sides of the remaining portion of the fin structure.
 13. The method of claim 10, further comprising forming a gate dielectric layer over the oxide layer.
 14. A method comprising: forming a fin structure over a substrate, wherein the fin structure comprises a bottom portion, a middle portion over the bottom portion and a top portion over the middle portion, wherein the top portion and the middle portion are made of different materials; forming a liner layer laterally surrounding the bottom portion and the middle portion of the fin structure, and spaced apart from the top portion of the fin structure; forming an isolation feature over the liner layer such that the isolation feature is spaced apart from the bottom portion of the fin structure and in contact with the top portion of the fin structure; recessing the liner layer and the isolation feature to expose sidewalls of the middle portion and the top portion of the fin structure; after recessing the liner layer and the isolation feature, forming a capping layer over the sidewalls of the middle portion and the top portion of the fin structure; and oxidizing the top portion of the fin structure and the capping layer to form an oxide layer over the fin structure.
 15. The method of claim 14, wherein the top portion of the fin structure has a material substantially the same as the capping layer.
 16. The method of claim 14, wherein the top portion of the fin structure is formed from silicon.
 17. The method of claim 14, wherein the middle portion of the fin structure is formed from silicon germanium.
 18. The method of claim 14, wherein the capping layer is formed by using an ALD process or a plasma enhanced ALD (PEALD) process.
 19. The method of claim 14, wherein forming the capping layer is such that the capping layer is thinner than the top portion of the fin structure.
 20. The method of claim 14, further comprising forming a gate dielectric layer over the oxide layer. 